The present invention relates generally to integrated circuit (IC) designs, and more particularly to an electrostatic discharge (ESD) protection circuit for a mixed-voltage semiconductor device.
ESD is one of the most prevalent causes for chip failures in both chip manufacturing and field operations. ESD can occur when the charges stored in machines or human bodies are discharged to the chip on contact or by static induction. A person can develop a very high static voltage, from a few hundred to several thousand volts, simply by walking across a room or by removing an IC from its plastic package, even when careful handling procedures are followed. The inadvertent presence of a sudden voltage spike in an IC can cause physical destruction of circuit features. The impact of ESD damage due to handling and testing can have a significant influence on the product yield.
Another issue that gives increasing importance to ESD control is the move towards replaceable ICs in electronic systems. Instead of replacing the whole circuit board, as used to be the standard practice, users are now encouraged to purchase upgrades to their microprocessors and memory cards and perform the installation themselves. Since the installation does not necessarily take place in an ESD-safe environment, the ICs need to be ESD robust.
An ESD protection circuit can be implemented for providing an energy dissipation path during an ESD event. As IC's become more complicated and, as a result, denser, the metal-oxide-semiconductor (MOS) circuit elements that make up the IC must become smaller. As the size of a MOS circuit element shrinks, its operating voltage also tends to drop. These elements operating with the lower voltage often need to interface with other circuit modules operating with higher voltages. The ESD protection circuits implemented for the MOS circuit elements operating with the lower voltage must be able to avoid having the oxides overstressed by the higher voltage of the other circuit modules during normal operation. At the same time, the ESD protection circuits must be turned on to provide an ESD current dissipation path during an ESD event. Because of the importance of ESD protection, it is desirable to improve and provide alternative ESD protection circuits.
As such, what is needed is an improved ESD protection circuit for a mixed-voltage semiconductor device.